I think you would be very disappointed with the ASP.NET support in Dreamweaver. You would be MUCH better off getting yourself a copy of Visual Studio / Web Developer (express editions are free) and doing your development there.

That said, there's no reason why you can't create your HTML and CSS in Dreamweaver, then bring those files into Visual Studio to actually put in the code. This is kind of a one-time deal though since usually once you've started splitting up your HTML into master pages and user controls/partial views, it's pretty difficult to go back and edit them again in Dreamweaver.